1. Field of the Invention
Embodiments of the present invention generally relate to a slurry delivery method and apparatus for polishing a substrate in a chemical mechanical polishing system.
2. Description of the Related Art
Chemical mechanical planarization, or chemical mechanical polishing (CMP), is a common technique used to planarize substrates. In conventional CMP techniques, a substrate carrier or polishing head is mounted on a carrier assembly and positioned in contact with a polishing article in a CMP apparatus. The carrier assembly provides a controllable pressure to the substrate urging the substrate against the polishing article. The article is moved relative to the substrate by an external driving force. Thus, the CMP apparatus effects polishing or rubbing movement between the surface of the substrate and the polishing article while dispersing a polishing composition to effect both chemical activity and mechanical activity.
Chemical mechanical planarization systems generally utilize a polishing head to retain and press a substrate against a polishing surface of a polishing material while providing motion therebetween. Some planarization systems utilize a polishing head that is moveable over a stationary platen that supports the polishing material. Other systems utilize different configurations including a rotating platen to provide relative motion between the polishing material and the substrate. A polishing fluid is typically disposed between the substrate and the polishing material during polishing to provide chemical activity that assists in the removal of material from the substrate. Some polishing fluids may also contain abrasives.
One of the challenges in developing robust polishing systems and processes is providing uniform material removal across the polished surface of the substrate. For example, as the substrate travels across the polishing surface, the edge of the substrate is often polished at a higher rate. This is due in part to the tendency of the substrate to nose drive, that is, centrifugal and frictional forces force the substrate to move toward to exterior of the support surface as the substrate moves across the support surface.
An additional problem with polishing uniformity is the distribution of slurry on the polishing surface. If the slurry is unevenly distributed, the polishing surface may not evenly polish across the substrate surface. If too little slurry is used, the polishing surface may distort the features of the substrate surface. If too much slurry is applied, valuable slurry may be wasted. Therefore, a system for delivering a polishing fluid to a chemical mechanical polishing surface that adjustably distributes and conserves slurry is needed. As the slurry leaves the slurry distribution system, the pressure drop across the system may facilitate the production of gas bubbles in the line. To provide delivery that is uniform and not distorted by the production of gas bubbles is an important process development goal.